Effect of gamma irradiation and storage on lutein and zeaxanthinin liquid, frozen and dried egg yolk samples

Mine Uygun-Sarıbay • Ece Ergun • Turhan Koseoglu

Received: 29 January 2014

� Akademiai Kiado, Budapest, Hungary 2014

Abstract The aim of this study was to monitor the effects

of gamma irradiation and storage on the content of lutein

and zeaxanthin in egg yolk samples. Liquid, frozen and

dried egg samples were subjected to gamma irradiation

doses of 0, 1, 2 and 3 kGy followed by storage of liquid

samples at ?4 ± 1 �C for 21 days, frozen samples at

-18 ± 1 �C and dried samples at room temperature for

1 year. The xanthophyll concentrations were determined

by high-performance liquid chromatography-diode array

detector. It was observed that concentrations of both lutein

and zeaxanthin were decreased significantly (P \ 0.05)

after irradiation and during storage. The mechanism for

radiation-induced degradation was proposed as radical

formation which initiate chain reactions. It was suggested

that during storage active radical species and oxygen

caused the degradation.

Keywords Egg yolk � Gamma irradiation � Lutein �Zeaxanthin � Storage

Introduction

Food irradiation is a process of treating food in order to

eliminate food-borne pathogens, make it safer to eat and

have a longer shelf life. Food can be irradiated by exposing

it to the gamma rays of a radioisotope (i.e. 137Cs and 60Co),

energetic electrons from partical accelerators, and X-rays.

These are suitable source of ionizing energy for the food

irradiation applications because they have enough energy

to penetrate a considerable thickness of food products.

An extensive review of science related to microbiological

safety indicates that irradiation is an effective solution to

the problem of microbial contamination. Irradiation is

accepted as a food safety process by independent health

organizations and regulatory agencies around the world [1].

At present, specific applications of food irradiation are

approved by national legislations in over 55 countries

worldwide [2].

Egg is known to be an excellent source of high-quality

proteins, lipids, vitamins and minerals. Besides the direct

consumption, egg is used as ingredient in foods due to the

functional properties of the yolk and white such as flavor,

color, foaming, emulsifying, binding, thickening and lea-

vening. However, eggs are responsible for causing food-

born illnesses when contaminated by different microor-

ganisms, among which Salmonella enteritidis is most sig-

nificant. The processes such as rapid cooling, washing with

antimicrobial solutions and heat pasteurization can be used

in order to reduce external and internal contamination of

egg and egg-containing products.

Ionizing radiation at medium doses can also reduce or

eliminate pathogens in eggs. Food and Drug Administration

(FDA) has approved irradiation of eggs at doses up to 3 kGy.

However, it is important to examine the changes in chemical

and sensory characteristics. In order to investigate the effect of

irradiation, radiation induced changes in chemical, physico-

chemical and functional properties such as pH, viscosity,

color, texture, foaming ability, emulsion capacity and total

carotenoid of egg samples have been determined by several

reseachers [3–9]. However, no study has been directly

examined the effect of irradiation on lutein and zeaxanthin,

the most abundant xanthophylls found in egg yolk and

responsible for the yellow color. These xanthophylls are the

two major components of the macular pigment of the retina

M. Uygun-Sarıbay � E. Ergun (&) � T. Koseoglu

TAEA, Saraykoy Nuclear Research and Training Center,

Kazan 06983, Ankara, Turkey

e-mail: ece.ergun@taek.gov.tr

123

J Radioanal Nucl Chem

DOI 10.1007/s10967-014-3171-5

and have dual functions; to act as powerful antioxidants and

to help protect eyes against damage due to ultraviolet radia-

tion from the sun [10]. They are not produced in the body and

must be consumed through diet. The yolks of chicken eggs

involve different amounts of lutein and zeaxanthin due to the

genetic variations and husbandry conditions [11].

Lutein and zeaxanthin are both dihydroxy-carotenoids

having conjugated trans double bonds with the ionone ring

systems being substituted at both the 3 and 30 carbon

(Fig. 1). In zeaxanthin, the ionone rings are both b types

and the b-ionone ring double bond is found between the C5

and C6 carbons so that all double bonds are conjugated

with the polyene chain. On the other hand, lutein has both a

b-ionone ring and an e-ionone ring. The e-ionone ring has a

C4–C5 double bond and an allylic 30-hydroxyl group [12].

These structural properties play an important role in the

oxidation and degradation of these xanthophylls.

Recent studies have been indicated that carotenoids are

susceptible to ionizing radiation, but this effect has been

investigated by total carotenoid analysis and color measure-

ments [4, 7]. None of these studies directly monitor the

radiation-induced degradation of lutein and zeaxanthin, and

discuss the degradation mechanism. The main objective of

this study is to identify the effect of gamma irradiation on the

content of lutein and zeaxanthin present in commercial liquid,

frozen and dried egg yolks by high-performance liquid

chromatography-diode array detector (HPLC-DAD). The

effect of storage on these xanthophylls is also examined.

In addition, mechanisms are proposed for the degradation of

lutein and zeaxanthin.

Experimental

Chemicals and standards

Tert-butyl methyl ether (TBME), methanol, ethyl acetate,

petroleum ether and triethyl amine were purchased from

Merck (Darmstadt, Germany). High-purity water was pre-

pared with a Milli-Q Gradient water-purification system

(Millipore, Eschborn, Germany). Before High Performance

Liquid Chromatography (HPLC) analysis, all solvents were

degassed by ultrasonic treatment (Bandelin Sonorex,

Berlin, Germany). Pure lutein (Rotichrom�) and zeaxan-

thin (Rotichrom�) standards were purchased from Carl

Roth (Karlsruhe, Germany).

Samples, irradiation and storage

Liquid and dried egg yolk samples were supplied from AB

Foods Inc. (Balıkesir, Turkey). A certain amount of liquid

egg samples had been frozen immediately at -18 ± 1 �C

in a freezer (Beko 3400 CF, Turkey). All egg samples

(liquid, frozen and dried) were exposed to ionizing radia-

tion using tote-box type irradiator equipped with 60Co

gamma source (SVST-1 category IV) at Turkish Atomic

Energy Authority, Saraykoy Nuclear Research and Train-

ing Center (Ankara, Turkey). Irradiation was performed at

doses of 0, 1, 2 and 3 kGy at ambient temperature and

atmosphere without any gas introduction. Irradiated liquid

egg samples were stored at ?4 ± 1 �C for 21 days and

analyses were performed on day 0, 7, 14, 21. Frozen and

dried egg samples were stored for 1 year at -18 ± 1 �C

and at room temperature, respectively. Analyses of these

samples were carried out at 0, 3, 6, 9, 12 months. Sample

containers were covered with aluminum foil during storage

in darkness in order to avoid photooxidation. The dose

distribution was measured using dichromate dosimeter

(Harwell Gammachrome, UK).

HPLC analysis of lutein and zeaxanthin

The extraction and quantification of lutein and zeaxanthin

were carried out using previously published methods, with

minor modifications [13, 14]. Aliquots (1 g) of irradiated

and non-irradiated liquid, frozen and dried egg yolks were

Fig. 1 The structures of lutein

and zeaxanthin

J Radioanal Nucl Chem

123

poured directly into a separating funnel. A ternary solvent

mixture (methanol/ethyl acetate/petroleum ether, 1:1:1,

v/v/v) was added and shaken gently. The supernatant was

collected in a round-bottom flask. This procedure was

repeated until the sample became colorless. The mixture

was evaporated to dryness on a rotary evaporator at 30 �C.

The residue was then dissolved in 5 ml of TBME/methanol

mixture (1:1, v/v), filtered through a 0.45 lm membrane

filter and filled in amber USP Type I vial. The samples

were immediately analysed using HPLC-DAD system

consisting of Waters Alliance 2695 (Eschborn, Germany)

separation module with Waters 2996 photodiode array

dedector. The analytical scale separation was developed

on a C30 column (5 lm, 250 9 4.6 mm, YMC Europa

GmbH, Dinslaken Wilmington, NC) and column was kept

at 35 �C. The mobile phases were methanol/purified water/

triethyl amine (90/10/0.1, v/v/v, eluent A) and TBME/

methanol/purified water/triethyl amine (90/6/4/0.1, v/v/v/v,

eluent B). The gradient procedure, at flow rate of 1.0 mL/

min, was as follows: (1) start at 93.5 % eluent A and 6.5 %

eluent B (2) a 34-min linear gradient to 100 % eluent B (3)

a 4-min linear gradient back to 93.5 % eluent A and 6.5 %

eluent B (4) a 5-min hold at 93.5 % eluent A and 6.5 %

eluent B.

Calibration was performed in the range of 0.5–10 lg/ml

using dilutions of the respective stock solutions of lutein

and zeaxanthin in methanol. Calibration graphs were con-

structed by plotting the respective peak areas (450 nm,

mAUs) against the concentrations (lg/ml). Coefficients of

determination were always higher than 0.997.

Peak identification was based on comperisons with

retention time of lutein and zeaxanthin standards. Quanti-

fication was carried out by integrating peak areas in the

HPLC chromatograms. All HPLC analyses were performed

in triplicate.

Statistical analysis

Quantitative data were presented as mean ± SD of at least

triplicate experiments. Means were compared according to

Duncan’s multiple-range test [15]. The significant statisti-

cal level was set to P \ 0.05.

Results and discussion

Effect of irradiation on lutein and zeaxanthin

The application of ionizing radiation on eggs in order to

reduce and eliminate Salmonella can cause changes in lutein

and zeaxanthin content. The amount of lutein and zeaxanthin

loss due to the irradiation is affected by several factors,

including dose, temperature, presence of oxygen, and sample

type. Therefore, to investigate this effect, liquid, frozen and

dried egg yolk samples were irradiated at doses of 0, 1, 2 and

3 kGy, and lutein and zeaxanthin concentrations of these

samples were determined using HPLC-DAD. Representative

HPLC chromatograms are shown in Fig. 2. Satisfactory

separation was obtained and proper identification and quan-

tification for lutein (retention time = 15.5 min) and zeaxan-

thin (retention time = 16.8 min) was carried out. Table 1

summarizes the amounts of lutein and zeaxanthin in irradiated

and non-irradiated egg yolk samples and the effect of storage.

The amounts of lutein and zeaxanthin were found to be

4.45 ± 0.08 and 2.18 ± 0.07 lg/g of non-irradiated liquid

egg yolk, respectively. However, xanthophyll contents in

liquid sample were decreased significantly with increasing

irradiation dose (at 3 kGy, 2.17 ± 0.06 lg/g for lutein and

1.02 ± 0.03 lg/g for zeaxanthin, P \ 0.05). It was observed

that after irradiation at dose of 3 kGy, *51 % of lutein and

*53 % of zeaxanthin were degraded in liquid egg yolk

samples. On the other hand, radiation-induced degradation of

lutein and zeaxanthin in frozen and dried egg yolk samples

was much less than in liquid samples. In frozen egg yolk

samples, the amounts of lutein and zeaxanthin were decreased

from 5.96 ± 0.08 to 5.08 ± 0.08 lg/g (*15 % degraded)

and from 1.37 ± 0.10 to 1.11 ± 0.05 lg/g (*19 % degra-

ded), respectively. In dried egg yolk samples, the results

indicated that *23 % of lutein and *25 % of zeaxanthin

were degraded after irradiation at dose of 3 kGy.

Losses of xanthophylls can be explained by two mech-

anisms commonly called direct and indirect effects of

radiation on molecules. Direct effect could be responsible

for the losses of lutein and zeaxanthin in dried samples.

The energy absorbed from ionizing radiation gives rise to

formation of ions and excited xanthophylls (Eq. 1) which

may decompose into radicals. Therefore, the initial reaction

mechanism could be the ion dissociation giving a radical

(Eq. 2), ion–molecule reaction (Eq. 3), germinate recom-

bination of ions (Eq. 4), dissipation of excitation energy

without reaction (Eq. 5) dissociation of excited molecules

to radical products (Eq. 6) and recombination of radicals

(Eq. 7) [16].

XH�!c XHþ; e�; XH� ð1Þ

XHþ ! X�þ þ H� ð2Þ

X�þ þ XH! XHþ þ X� ð3Þ

XHþ þ e� ! XH� ð4ÞXH� ! XH ð5ÞXH� ! X� þ H� ð6ÞX� þ H� ! XH ð7Þ

X� and H� radicals are formed through homolytic cleavage

of the weakest bonds. Previous report [17] indicates that for

J Radioanal Nucl Chem

123

zeaxanthin C4–H, C40–H bonds in the b-ionone rings have

the lowest dissociation energy. However, for lutein, C60–H

bond in the e-ionone ring is the weakest bond. The reason

could be the conjugated C=C double bonds which

decreases the dissociation energy of the allylic hydrogen.

On the other hand, hydrogen can easily be abstracted from

a saturated carbon atom in a position allylic to the polyene

chain [18]. However, the bond dissociation energy of 9a

and 13a positions is approximately 0.6 eV higher than the

lowest bond dissociation energy reported in the paper [17].

Since the samples were irradiated at low dose values,

molecules could not be damaged so severely, small

amounts of radical could be formed, and recombination of

these radicals might be the main reaction mechanism rather

than diffusion from the spurs into the bulk. However,

irradiation was carried out at ambient atmosphere (in the

Fig. 2 Representative HPLC-DAD chromatogram of a lutein calibration solution, b zeaxanthin calibration solution, c non-irradiated egg yolk

extract, d irradiated egg yolk extract

J Radioanal Nucl Chem

123

presence of oxygen). Thus the most probable route is the

reaction of oxygen with the radical species. According to

this reaction both X� and H� radicals are converted into

peroxyl radicals (Eqs. 8, 9).

X� þ O2 ! XOO� ð8ÞH� þ O2 ! HOO� ð9Þ

Peroxyl transients can attack polyene chain which is

susceptible to radical attack due to the delocalisation of

p-electrons. After that, the stable final products (epoxides

and carbonyls) can be produced [19]. The proposed

mechanisms are given in Eqs. 10–16.

XOO� þ XH! XO2XH� ð10ÞXO2XH� ! XO� þ epoxide ð11ÞXO� þ XH! XOXH� ð12ÞXOXH� þ O2 ! XOXHO�2 ð13Þ

Table 1 Lutein and zeaxanthin in irradiated and non-irradiated liquid, frozen and dried egg yolk samples during storage. Mean value and

standard error (n = 3)

Sample Storage Lutein (lg g-1 sample)/irradiation dose (kGy)

0 1 2 3

Liquid egg yolk 0x 4.45a ± 0.08 4.26b ± 0.07 3.28def ± 0.10 2.17h ± 0.06

7x 3.80c ± 0.07 3.42d ± 0.08 2.19h ± 0.02 1.66j ± 0.04

14x 3.36de ± 0.04 3.26ef ± 0.06 2.10h ± 0.07 1.51k ± 0.06

21x 3.21f ± 0.08 2.71g ± 0.03 1.96i ± 0.04 1.34l ± 0.03

Frozen egg yolk 0y 5.96a ± 0.08 5.78a ± 0.05 5.41bc ± 0.11 5.08de ± 0.08

3y 5.81a ± 0.07 5.68ab ± 0.07 4.98de ± 0.04 4.86def ± 0.04

6y 5.13cd ± 0.08 4.76efg ± 0.06 4.52ch ± 0.04 4.37h ± 0.03

9y 4.95de ± 0.07 4.61de ± 0.07 4.42h ± 0.06 4.50gh ± 0.07

12y 4.77efg ± 0.05 4.59fgh ± 0.06 4.44ch ± 0.03 4.26h ± 0.07

Dried egg yolk 0z 8.84a ± 0.12 8.33b ± 0.08 7.23d ± 0.07 6.84e ± 0.06

3z 7.64c ± 0.09 6.27g ± 0.07 4.84j ± 0.06 3.71m ± 0.05

6z 6.32f ± 0.06 5.65h ± 0.05 4.39k ± 0.04 3.06n ± 0.03

9z 5.60h ± 0.08 4.89ı ± 0.07 4.09l ± 0.05 2.86o ± 0.04

12z 4.76j ± 0.05 4.38k ± 0.04 3.64m ± 0.02 2.47p ± 0.07

Sample Storage Zeaxanthin (lg g-1 sample)/irradiation dose (kGy)

0 1 2 3

Liquid egg yolk 0x 2.18a ± 0.07 1.98b ± 0.08 1.25cde ± 0.06 1.02de ± 0.03

7x 1.88c ± 0.09 1.65bc ± 0.06 1.01de ± 0.04 0.89de ± 0.04

14x 1.69bc ± 0.06 1.45bcd ± 0.09 0.92de ± 0.03 0.77e ± 0,04

21x 1.64bc ± 0.05 1.29cde ± 0.11 0.84de ± 0.07 0.65f ± 0,05

Frozen egg yolk 0y 1.37ab ± 0.10 1.23abc ± 0.03 1.19bcd ± 0.02 1.11cdef ± 0.05

3y 1.38a ± 0.08 1.22abc ± 0.07 1.08cdef ± 0.10 0.98ef ± 0.08

6y 1.33ab ± 0.03 1.20abc ± 0.06 1.10cdef ± 0.09 1.01def ± 0.07

9y 1.23abc ± 0.06 1.21abc ± 0.10 1.11cdef ± 0.07 0.95f ± 0.13

12y 1.20abc ± 0.08 1.14cde ± 0.07 1.06cdef ± 0,07 0.97ef ± 0.08

Dried egg yolk 0z 1.91a ± 0.07 1.80ab ± 0.04 1.64bcd ± 0.06 1.43fgh ± 0.13

3z 1.80ab ± 0.10 1.66bc ± 0.03 1.54cdefg ± 0.05 1.29hij ± 0.08

6z 1.63cde ± 0.08 1.60cdef ± 0.03 1.44fgh ± 0.03 1.26ijk ± 0.08

9z 1.53cdefg ± 0.03 1.62cde ± 0.07 1.42ghi ± 0.08 1.18jk ± 0.11

12z 1.46efgh ± 0.05 1.47defg ± 0.04 1.30hij ± 0.11 1.10k ± 0.03

x Day, 4 ± 1 �Cy Month, -18 ± 1 �Cz Month, room temperature

Means with different superscript letters are significantly different (P \ 0.05)

J Radioanal Nucl Chem

123

XOXHO�2 þ XH! XOXHO2XH� ð14Þ

XOXHO2XH� ! XOXHO� þ epoxide ð15ÞXOXHO� ! X� þ 2 carbonyls ð16Þ

However, in aqueous samples another effect called ‘indi-

rect effect’ should be considered. When an aqueous system

is irradiated, water absorbs large fraction of the radiation

energy and very reactive species namely hydroxyl and

hydrogen radicals, hydrated electrons and molecular pro-

ducts (hydrogen and hydrogen peroxide) are formed [16].

These radical species could react with lutein and zeaxan-

thin and cause degradation. Hydrogen radicals, hydrated

electrons acts as reducing agents in air-free media, but in

the presence of oxygen these species are converted into

peroxyl radicals (Eqs. 9, 17).

e�sol þ O2 ! O��2 ð17Þ

Therefore, peroxy and hydroxyl radicals act as oxidizing

transients. However, hydroxyl radicals are more powerful

oxidants than peroxyl radicals and participate in a number

of reactions such as addition, electron transfer and H-atom

abstraction reactions. Hydroxyl radicals can readily attack

to the double bonds of the xanthophylls and generate a

radical site on the molecule. The resulting radical adducts

can also scavenge oxygen. However, these peroxyl tran-

sients are rather unsable and can undergo hydrolysis

forming various final products (Eqs. 18, 19).

XHþ �OHþ �XHOH ð18Þ�XHOHþ O2 ! �OOXOH! XOHþ HO�2 ð19Þ

Hydroxyl transients can also react with lutein and zea-

xanthin abstracting a hydrogen yielding a free radical of

xanthophylls (Eq. 20). It is easier for xanthophylls to give

hydrogen to hydroxyl radicals having a high reduction

potential than to alkyl peroxy radicals [20].

XHþ �OH! X� þ H2O ð20Þ

Xanthophyll radicals can add oxygen (Eq. 8) and further

reactions (Eqs. 10–16) can take place.

In dried egg yolk samples, direct effect of ionizing

radiation could be the main mechanism for the degradation

of lutein and zeaxanthin. On the other hand, in aqueous

samples (liquid and frozen egg yolks) xanthophyll

destruction is expected to be more effective due to the

radiolysis products of water. However, in frozen samples,

radicals diffuse much more slowly due to the lower tem-

perature. They are trapped in the frozen material, tend to

recombine to form the original substances rather than dif-

fuse through the food and react with other components.

Therefore, loss of lutein and zeaxanthin was reduced when

egg samples were irradiated in frozen state. Eventually,

reduction in the amounts of lutein and zeaxanthin in liquid

egg yolk samples were much greater than in dried and

frozen samples (Fig. 3).

Effect of storage on lutein and zeaxanthin

In this study, the effect of storage on amount of lutein and

zeaxanthin in irradiated and non-irradiated egg yolk sam-

ples was also monitored. The results indicated that amount

of lutein significantly (P \ 0.05) decreased for both irra-

diated and non-irradiated liquid samples (Table 1, Fig. 4a).

It was observed that in non-irradiated liquid sample,

*28 % of lutein was degraded during a 21 day storage

period. In irradiated liquid samples, loss of lutein after

storage was *36 %, *40 % and *38 % at dose of 1, 2

and 3 kGy, respectively. On the other hand, percentages of

lutein loss obtained in irradiated and non-irradiated dried

samples were *46 %, *47 %, *49 % and *64 % at

dose of 0, 1, 2 and 3 kGy, respectively (Table 1, Fig. 4c).

However, lutein was degraded much less in frozen samples

(*20 %, *21 %, *18 % and *16 % at dose of 0, 1, 2

and 3 kGy, respectively) after the same storage period

(Table 1, Fig. 4b).

The results indicated that minimum zeaxanthin degra-

dation also occurred in frozen samples after storage. It was

observed that in frozen samples during a 12 month storage

period, *13 %, *7 %, *11 % and *14 % of zeaxanthin

was degraded at dose of 0, 1, 2 and 3 kGy, respectively

(Table 1, Fig. 5b). However, after the same storage period,

Fig. 3 Effect of irradiation on the amount of a lutein b zeaxanthin in

liquid, frozen and dried egg yolk samples

J Radioanal Nucl Chem

123

losses of zeaxanthin in dried samples at dose of 0, 1, 2 and

3 kGy were found to be *24 %, *18 %, *21 %,

*23 %, respectively (Table 1, Fig. 5c). On the other hand,

percentages of zeaxanthin loss obtained in irradiated

and non-irradiated liquid samples were *25 %, *35 %,

*33 %, *36 % (Table 1, Fig. 5a).

Degradation of non-irradiated lutein and zeaxanthin

during storage was due to the oxidation of these xantho-

phylls under the influence of atmospheric oxygen. The

efficiency of oxidative degradation is affected by the light

conditions, temperature, oxygen availability, moisture

content [21]. Oxygen and light exposure during storage

were prevented by properly sealing the samples in dark

packaging and by keeping the samples in the dark so that

only the oxygen present in the container can have caused

the oxidation. In order to monitor the oxidative degrada-

tion, samples were stored without purging with nitrogen or

any inert gas. Therefore, the oxidative degradation of non-

irradiated samples was mainly affected by the concentra-

tion of oxygen in the container, temperature and moisture

content. The influence of water activity on oxidation is

studied by several reseachers. It has been evidenced that

the lower water activity increases the b-carotene degrada-

tion [22, 23], cholesterol oxidation [24]. Therefore, non-

irradiated dried samples (low water activity) were much

more degraded than non-irradiated frozen samples over a

12 month period. Furthermore, thermal process and storage

at higher temperature (room temperature) can cause the all-

trans-isomer to the cis-isomer in dried samples. It is sup-

posed that isomerisation could be the first step of oxidation,

leading to a diradical of carotenoids which can easily be

attacked by oxygen on either side of the cis bond. This

radical attack followed by homolytic internal substitution

gives the epoxides, apocarotenones and apocarotenals [25].

Fig. 4 Effect of storage on the amount of lutein in a liquid, b frozen

and c dried egg yolk samples

Fig. 5 Effect of storage on the amount of zeaxanthin in a liquid,

b frozen and c dried egg yolk samples

J Radioanal Nucl Chem

123

Therefore, lower temperature (-18 ± 1 �C in a freezer)

may have helped to reduce the degradation of lutein and

zeaxanthin during 12 months of storage of non-irradiated

frozen samples. However, degradation of non-irradiated

liquid samples were also high despite the short storage

period and high water content. High-water content may

increase the rate of oxidation by enhancing the mobility of

reactants and the solubility of oxygen in foods.

Same results were obtained for irradiated liquid, frozen

and dried samples. The least degradation occurred in frozen

samples. In irradiated samples, besides the effects

mentioned above, active radicals which do not undergo

recombination during the initial storage period can play an

important role in the degradation of lutein and zeaxanthin.

It was observed that this effect was much more remarkable

for liquid samples due to the short storage period and active

products of water radiolysis. After the 21 day storage

period, degradation of lutein and zeaxanthin was more

effective in irradiated liquid samples than in non-irradiated

liquid samples.

Conclusions

Lutein and zeaxanthin belong to the xanthophyll family of

carotenoids and are the two major components found in

egg yolks. They are considered as powerful antioxidants

due to their singlet oxygen quenching abilities. In addition,

they are efficient in scavenging free radicals. Therefore,

they are important nutrients for human that need to be

consumed to reduce the potential damage in the cells.

However, application ionizing radiation on eggs in order to

reduce the microorganisms causes degradation of these

xanthophylls. Thus, it is important to monitor and identify

the effect of ionizing radiation on these molecules.

Degradation mechanism and the proportions of reactive

species depend on the irradiation conditions and nature of

the material being irradiated [16]. Therefore, three types of

egg samples (liquid, frozen and dried) were irradiated at

dose of 0, 1, 2 and 3 kGy at ambient conditions. After each

irradiation, concentrations of lutein and zeaxanthin were

determined by HPLC-DAD. It was observed that with

increasing doses, lutein and zeaxanthin contents of egg

samples were decreased significantly (P \ 0.05). It was

suggested that absorption of radiation energy gave rise to

radical formation and in the presence of oxygen these

radical species were converted into peroxyl transients and

stable final products (epoxides and carbonyls). The greatest

losses of lutein and zeaxanthin were found in liquid sam-

ples due to the radiolysis products of water. However, in

frozen samples, chemical changes were reduced due to the

lower mobility of free radicals.

Effect of storage on both irradiated and non-irradiated

samples were also monitored. During the storage period of

non-irradiated samples, lutein and zeaxanthin were degra-

ded due to the interaction of xanthophylls and oxygen.

However, the degradation rate of lutein and zeaxanthin in

irradiated liquid samples was higher than in non-irradiated

liquid samples. It was attributed to life time and activity of

radical species.

Acknowledgment Authors wish to express their gratitude to

Turkish Atomic Energy Authority (TAEK-A3.H1.P1.01), which

financially supported this work.

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